1. Field of the Invention
This invention relates to a broadcasting system which provides one-to-many communication service and, in particular, to a broadcasting system which is capable of broadcasting common contents concerned with push type service to a plurality of subscriber""s terminals.
2. Description of the Related Art
In the past, performance of processing in a computer and technology of network communication have been remarkably improved. As a result, recent attention has been focused on multimedia technology which employs bi-directional media and a combination of sounds, characters, and images. On-demand type service is one of the services which are provided by the multimedia technology.
In a network system which provides on-demand type service, terminal devices and a center device are connected to a ground network, such as a cable television network. When a user sends a receiving request or a retrieving request from one of the terminal devices to the control device, contents which include service information in response to the user""s request are transmitted from the center device to the terminal device of the user by accessing databases in the center device. Thereby, the user may obtain the contents in reply to the user""s request.
The internet has widely and quickly grown up and has built a communication infrastructure which is not less than a public telephone network, by repeating mutual connection of Local Area Network (hereinafter, referred to as LAN). The above described on-demand type service may easily provide with more sophisticated service at a low cost by using the Internet. In addition to the on-demand type service, push type service which can broadcast common contents to a plurality of subscriber""s terminals has also been considered and started with interest.
The push type service is more suitable for achieving efficiency of network communication and saving communication cost when the service employs a satellite communication network rather than employs a ground communication network since the service provides broadcasting. However, to commercialize the value added service which provides satellite television broadcasting or satellite data communication using the broadcasting, only users subscribing to the service can enjoy selectively the service.
In the broadcasting system which uses the satellite communication network, a temporary key is used for transmitting broadcasting information to users, and a unique user key is used for each receiving terminal. The temporary key is updated periodically to maintain confidentiality of the broadcasting information. The user key is used when the temporary key is initialized in starting up the receiving terminal of the temporary key is modified. Therefore, an information sending device may broadcast the encrypted information to each receiving device via a satellite communication network by selecting any keys among these keys. Each of the receiving terminals may receive the information and accumulate the information by decoding the encrypted information using these keys. According to the above techniques, only users who are subscribing to the service may receive the information and a probability that an imprudent or an illegal person receives the information may be considerably reduced.
A technology about such a broadcasting system which attaches importance to confidentiality is also disclosed in Japanese Laid-Open Publication No. Hei 8-293827 (namely, 293827/1996) titled xe2x80x9cA Satellite Information Broadcasting System and A Receiving Device Used in The Systemxe2x80x9d.
The above-mentioned technology used in the satellite Internet system via a satellite communication network is a technology in which a function of a IP (Internet Protocol: hereinafter, referred to as IP) router, which is widely used in a ground network, is applied to the satellite communication network. However, since protocols, such as TCP/IP (Transmission Control Protocol/Internet Protocol) and UDP/IP (User Datagram Protocol/Internet Protocol), have been developed on the basis of a point-to-point communication system, it is difficult to provide a broadcasting communication system which belongs to a point-to-multi-point communication system, as long as the protocols have been used.
Namely, since in the point-to-point communication system, a message is transmitted between a source port and a destination port each of which is assigned a unique IP address, the message should be copied, for example, in interchange nodes of a network between the interchange nodes along with a transmission path and be transmitted to a plurality of interchange nodes and, as a result, efficiency of transmission is degraded. Also, a work load of each of the interchange nodes is increased according to the above processes. Furthermore, if there are different destination nodes, the point-to-multi-point communication system which has been in a network can not be efficiently used since there are a plurality of nodes to which the interchange nodes should transmit the message.
Further, when a satellite communication network is used as infrastructure of a point-to-point communication system, there is a problem that the communication system can not provide a merit in an area where a land-based network is fully popularized, as a result, a running cost of the communication system becomes high.
Also, in a broadcasting system as disclosed in Japanese Laid-Open Publication No. Hei 8-293827, it is possible to maintain confidentiality of broadcasting information, but it is too expensive to install the system. If possible, it is desirable to divert an existing land-based LAN resources which has been used to communicate.
Therefore, it is an object of the invention to provide a broadcasting system which is capable of efficiently broadcasting by using present network protocols and outstanding confidentiality.
According to a first aspect of the invention, there is provided a broadcasting system which includes a source sending unit and a plurality of receiving terminals each of which is connected to the source sending unit via a network and which is operable to broadcast service contents from the source sending unit to the plurality of receiving terminals. Wherein, the source sending unit comprises a data packet generator which generates a data packet including a part of the service contents and a group address assigned to a predetermined group of the receiving terminals as a destination address, and a service contents delivering unit which delivers the data packet to the predetermined group of the receiving terminals based on the group address.
According to a second aspect of the invention, there is provided a broadcasting system which includes a source sending unit and a plurality of terminals each of which is connected to the source sending unit via a network and which broadcasts service contents from the source sending unit to the plurality of receiving terminals. Wherein, the source sending unit comprises a key supplying unit which generates a work key for each service of the service contents and sends the work key to the receiving terminals, a contents encrypting unit which encrypts the service contents by using the work key, and a contents delivering unit which delivers the encrypted service contents to the receiving terminals. Furthermore, each of the receiving terminals comprises a key receiving unit which receives the work key from the source sending unit, a contents receiving unit which receives the encrypted service contents from the source sending unit, and a contents decoding unit which decodes the received and encrytped service contents into decoded service contents.
According to a third aspect of the invention, there is provided a method of broadcasting service contents from a source sending unit to a plurality of receiving terminals each of which is connected to the source sending unit via a network. Wherein, the method comprises the steps of preparing the source sending unit, generating a data packet including a part of the service contents and a group address assigned to a predetermined group of the receiving terminals as a destination address, and broadcasting the data packet to the predetermined group of the receiving terminals on the basis of the group address.
According to a fourth aspect of the invention, there is provided a method of broadcasting service contents from a source sending unit to a plurality of receiving terminals each of which is connected to the source sending unit via a network. Wherein, the method comprises the steps of preparing the source sending unit, generating a work key for each service of the service contents and sending the work key to the receiving terminals, encrypting the service contents by using the work key, and delivering the encrypted service contents to the receiving terminals. Further, at each of the receiving terminals, the method comprises the steps of receiving the work key from the source sending unit, receiving the encrypted service contents from the source sending unit, and decoding the received and encrypted service contents.